Conjugated dienes from tertiary ethers



United States Patent"= f'"'() "ice 1 MM 1 z y Z primary or secondary, i.e. non-tertiary, and substituted 'ornon substituted. Thepreferred starting materials have 2,972 ,64s' H the mmula: 1m n CONJUGATED DIENES FROM TERTIARY ETHE o g R= o H.-a. Joseph A. Verdol, Dolton, and Russell W. Walker, r I 3 Lansing, 111., assignors to Sinclair Refining Company, I I g h I New York a col-Parana?! of Mame v where R is hydrogen or lower'alkyl, say of lto 8 carbon No Drawing. Filed May 20,,1959,,Ser. No. 814,380 10 atoms. Advantageously no R contains morethan 4 car- '7 l bon'atoms and the total number of carbon atoms are as 7 Claims' 260-481) noted beforel The alkoxy group is preferably methoxy or ethoxy, while the alkane is preferably derived from a g V C to C isoolefin found in a petroleum refinery product.

This invention'is a catalytic dehydrogenation "process Examples of somegtertiary ethers which are used in for making conjugated diene hydrocarbons from tertiary I this process are as follows: ethers. Conjugated dienes' are important intermediates g in the preparation of many valuable materials; for-exr CH ample, isoprene is currently of interest as a starting material for the manufacture of Synthetic Natural" rubt V her and butyl rubber. The preparation of diene hydro- Tertiaryamylmethyl ether carbons by this process has definite advantages over preo CHlCH:

'vious processes. The starting tertiary ethers, such as tertij Circa) Omens aryamylmethyl ether, tertiaryhexylmethyl ethers, etcl can be prepared in high purity from petroleum refinery l v mixed streams, using the method of copending Verdol aps j v Tertiaryamylethyl ether plication Serial No. 810,591, filed May 4, 1959. I CHiCHa CH1 When tertiary ethers from the aforementioned, process v v C'H3. C Q C H are employed in the process described herein, it is possit ble to prepare diene hydrocarbons of high purity,v since j v the purity of the diene in this process is dependent upon v V f i i the purity of the tertiary ether. The criterion ,of purity o s CHiCHi h is very important in the preparation of Synthetic' Natural CHE- OCH: V rubber, since the polymerization process involves the-use H CH of alkali metal and organo metallic catalysts which are j 2 a deactivated by certain impurities. Thempresentprocess a'mefliylv'a'methoxypentane therefore provides a method of preparing isoprene and, v i other conjugated dienes of the-purity necessaryfor cur-m; t ,r l CH:- rent and future commercial uses. v o o Prior art methods of making conjugated dienes fre- 9 2 methy1 '2 methoxypentane quently do not produce a pure product. For example, in j V OH'CH e 5 the catalytic dehydrogenation of paraffins, like isopentane, v v a .lQilfl'lifl'." impurities arise from accessory products' formed during H .Q a V. .W h the dehydrogenation reaction. The preparation of high g H; purity isoprene from isoamylenes by dehydrogenation is aphenylamethoxybutane -finery streams by the sulfuric acid process, since the en- 'invention in diene synthesis, the starting materials usually jetc.,-"and may be in ring,-i;e. aromatic' .oricycloaliphatic structures. l'-he alkoxy'group may be methoxyr brother r-eOR group containing up to about l2lorrnore cal-bon I. CH'r CH1.

atoms and may be alkyl including cycloalkyhor aromatic; .i m .mt3-mqthylel-butglla n also limited when the lsoamylenes are extracted from re- In accordance with this invention tertiary ethersof i defined structure are dehydrogenated in the presenceof steam or other inert gas to afford a conjugated diolefin vfrom the tertiary structure and an alcohol from the nontertiary structures of the ethers, Some unreacted tertiary ether and monoolefin may also be present in the; reactor efiluent s v The monoolefins can be separated from the eflluent and recycled with recovered and/ or fresh tertiary ether to produce"further quantitiesof the desired 'c'o'fitrained impurities in the isoamylenescause contamination of the isoprene. r

Where non-hydrocarbons have been used priortto this 5 are difunctional compounds such as ether alcohols (US. Patent 2,229,652), vinyl ethers (US. Patent 2,502,430) and esters, e.g. vinyl acetates, and diesters.. These. di-

. functional compounds are of necessity much more, err-p 5 pensive than the tertiary monoethers used in the process l d bim' "other usable inert gases 3 7 5???" of this invention. I A o 7 gen, CO CO, etc. The compounds used as starting materials in the proc- If For ex mp e, .i y y hy i l d lq f ess are ethers, alkoxy alkanes, of 6 to about 24 or more," hydrogenation in the presence of-commercial dehydropreferably 6 to 12 carbon atoms in whichjthe alkoxy or ..genation catalysts to afford a mixture of is'oprney s ether oXygen is attached to a b d h alkyl, 'amylenes, methanol and unreacted tertiar-yamylmethyl eluding cycloalkyl radical at ajtertiary carbon, that is, a vi hi .Ti. Ill .1. j TII'QIQLIQI' carbon which is attached to threeother carbon r'zatomsq- The tertiary carbon must be inan aliphaticjchainof ato lfQ a least 4 carbon atoms, and therefore the alkyl'will have at ammo-0011i C'Hfioacmofi least 5 carbon atoms to about 12 or more carbon atoms. Cris 0H? f 1 r .l The carbon atoms in the radical may be substituted with feitiawamflmethflether H MB ogmethyLbbutgfinon-reactivesubstitue'nts such as halogen, aryl-,. alkaryl',

- aeea es 3 v The m thanol s easily recovered from the reactor fluent aqueous layer by distillation. The isoprene can be separated from the non-aqueous effluent and the remaining mixture'ofisoam ylenes and unconverted, tertiaryamylr 4 mium oxide and pelleted. Catalysts of this type can be prepared as described in United States Patent No. 2,542,- 813. They can be regenerated with a mixture of steam and air in accordance with procedures which are well- Where the active catalytic material is supported, the support can be magnesia, zinc oxide, beryllium oxide, zirconium oxide, etc. Among the supported catalysts deriving their activity from the oxides of metals of atomic number from 26 to 29, inclusive, which can be employed -in=accordance with this invention, are those composed of the following amounts of the following materials by 5 methyl ethercan be recycled (with additional-freshmen- 5 known in the art. tiaryamylmethyl ether if desired) to produce further The Shell 205 catalyst is composed of a prequantities of isoprene. dominant amount of iron oxide and minor propor- A wide variety of catalysts is useful in carrying out the :tions of potassium oxide or carbonate and chromium process of this invention. Many of these are commeroxide. Analysis of the virgin catalyst was 44.2'percent cially available dehydrogenation catalysts which usualiron, 20.1 percent potassium, 1.52 percent chromium 1y derive their activity from'the oxides of metals having and 11.64 percent volatile material. Shell 105 catan atomic number from 24 to 29, inclusive,-that is, iron alyst, a similar type, can also be employed. Catalysts of oxide, copper oxide, chromium oxide, manganese oxide, this type can be made by mixing finely powdered calcined cobalt oxide, nickel oxide, singly or in combination, or ferric oxide, chromic oxide and potassium carbonate, wetmaterials giving these oxides upon calcination, supported ting, forming into pellets and calcining at 800 C. to or not supported on carriers. A specific usable catalyst 950 C. is composed of 72.4 weight percent MgO, 18.4 weight Various other catalysts which have dehydrogenating percent Fe O 4.6 weight percent CuO and 4.6 weight activity can be employed in the process but care must be percent K 0 and can be prepared by adding a solution taken when steam is used as the inert gas, to choose a of iron and copper sulfate to magnesium oxide suspendsteam-insensitive catalyst. Thus, catalysts prepared by ed in water, filtering the reacted mixture, washing the impregnating bauxite with about 5 percent by weight slurry with a solution of-potassium carbonate, drying and of barium hydroxide and/or strontium hydroxide may be calcining at 1200 F. Where unsupported iron oxide is used, in the presence of steam, potassium hydroxide beemployed as a catalyst, the catalyst will consist predoming employed as a promoter if so desired. inantly (from about 50 to 99.5 percent by weight) of 26 The conversion of the tertiary ether to, the conjugated iron Oxide Promoted with a minor amount (generally diene is accomplished by contacting the ether in the gasefrom about 0.5 to 20 percent by weight) of an alkali ous or vapor phase with the catalyst. This contacting metal oxide such as potassium oxide, sodium oxide, ruserves to break the. ether linkage without dehydrogenabidium Oxide, cesium Oxide, e ls g g S OX- tion in some molecules, leaving atertiary olefin which ides upon heating, as by calcination at about 750 to l200 30 may be recycled. Generally, the reaction temperature F. or more, for example, the carbonates or nitrates. Aluemployed will be within the range from about 1000 F. minum oxide, copper Oxi phosphorus oxides and zinc to 1250" F., while a range of about 1100 to 1200" F. is Oxide, generally in the amount of from about 2 i0 20 preferred Generally, the reaction pressure employed Percent y Weight, can e c uded in such catalysts as will be approximately atmospheric pressure. However, a stabilizer. Suitable catalysts of this type are composed th actio can also be carried out at subor superatof the following amounts of the following materials by mospheric pressures if desired.

weight. The reaction may be performed batchwise but prefer- TABLE I Catalyst Component Percent Component Percent Component Percent Component Percent 2 2 5 2 5 A1203"--. 2 1.5 5 A12O3. 15

ably the ether will be continuously fed to a fixed bed of the catalyst. The weight hourly space velocity can be in the range from about 0.1 to 5. The monoolefin hydrocarbons .can be separated from the reactor etfiuent and recycled in admixture with recovered and fresh tertiaryalkyl ether. This recycle can also be performed at a weight hourly space velocity within the range of about weight: 0.1 to 5, expressed in terms of weight units of tertiary TABLE II Catalyst 7 Component Parts Component Parts Component Parts Component Parts The Dow B catalyst used in the following examples is a calcium-nickel phosphate catalyst of the approximate formula Ca Ni(PO stabilized with chromium oxide. It is prepared by precipitating a solution of nickel and calcium chlorides with an ammonia-phosphoric acid solution. The flocculent precipitate is washed, filtered, dried, ground, mixed withw2 percent :by weight of chroether plus the weight units of monoolefin per weight unit of catalyst per hour.

The relative amounts of inert gas to tertiary ether (plus monoolefin hydrocarbon if any is recycled .or otherwise present) will ordinarily be within the, molar range of about 3 to 50:1, with ratios in the range of about 10 to 20:1 usually preferred.

The following examples of the process of this invention are intended to be illustrative only and not limiting.

Example I Tertiaryamylmethyl ether (B.P. 8687 C.) in admixture with steam was passed through a reactor charged with 200 grams of Shell 205 dehydrogenation catalyst. Before being introduced into the catalyst bed, the tertiaryamylmethyl ether and steam were preheated to a temperature of about 1150 F. and the catalyst bed was maintained at a temperature of 1100 to 1150 F. The space velocity was 0.8 (weight .units of tertiaryamylmethyl ether per weight unit of catalyst per hour) and 14.5 moles of steam per mole of tertiaryamylmethyl ether were employed in admixture with the tertiaryamylmethyl ether. This procedure was conducted for a period of 50 minutes. Analysis of the non-aqueous 'efliuent upon completion of the experiment showed the following weight percent distribution of products.

Unconverted tertiaryamylmethyl ether 18 C and lighter hydrocarbons 4 Analysis of the aqueous reactor eflluent showed the presence of 4.5 percent methanol.

Example 11 Tertiaryamyhnethyl ether (B.P. 86-87 C.) in admixture with steam was passed through a reactor charged with 108 gms. of Dow B dehydrogenation catalyst. Before being introduced into the catalystbed, the mixture of tertiaryamylmethyl ether and steam was preheated to a temperature of about 1060 F. The catalyst bed was maintained at a temperature of about 1060 to 1070 F. The space velocity was 0.8 (weight units of tertiaryamylmethyl ether per weight unit of catalyst per hour) and 15.7 moles of steam per mole of tertiaryamylmethyl ether were employed in admixture with the tertiaryamylmethyl ether. This procedure was conducted for a period of 15 minutes. Analysis of the non-aqueous reactor efliuent upon completion of the experiment showed the following weight percent distribution of products.

Analysis of the aqueous reactor efiiuent showed the pressure of 4 percent by weight of methanol.

We claim:

1. A method for making a conjugated diene which comprises contacting an alkoxy alkane in which the alkoxy group is attached to a tertiary carbon of an alkyl group of 5 to about 12 carbon atoms,v in the vapor phase with a dehydrogenating catalyst at a temperature of about 1000 F. to 1250 F. while the ether is in admixture with about 3.to 50 moles of an inert gas per mole of ether.

2. The process of claim 1 where the temperature is about 1100 to 1200 F.

3. The process of claim 1 where the inert gas is steam.

4. The process of claim 3 where the steam is present in an amount of about 10 to 20 moles per mole of ether.

5. The process of claim 3 where the ether is tertiaryamylmethyl ether.

6. The process of claim 3 where the catalyst is a calcium-nickel phosphate of the approximate formula Ca Ni(PO p 7. The process of claim 3 where the catalyst consists essentially of a predominant amount of iron oxide and minor proportions of potassium oxide and chromium oxide.

References Cited in the tile of this patent UNITED STATES PATENTS OTHER REFERENCES Marx: Chemical Abstracts, vol. 28,1934. columns 2322-3. 

1. A METHOD FOR MAKING A CONJUGATED DIENE WHICH COMPRISES CONTACTING AN ALKOXY ALKANE IN WHICH THE ALKOXY GROUP IS ATTACHED TO A TERTIARY CARBON OF AN ALKYL GROUP OF 5 TO ABOUT 12 CARBON ATOMS, IN THE VAPOR PHASE WITH A DEHYDROGENATING CATALYST AT A TEMPERATURE OF ABOUT 1000*F. TO 1250*F. WHILE THE ETHER IS IN ADMIXTURE WITH ABOUT 3 TO 50 MOLES OF AN INERT GAS PER MOLE OF ETHER. 